Turbine rotors with cooling arrangements are often found in turbo-machine construction, particularly in gas turbines. The disc requiring cooling generally comprises a shaft fitted with rotor blades and heat barrier segments. The cooling medium, generally air, is led along an annular space between a drum and a drum cover to the end face of the shaft and introduced into cooling openings in the end face. A radial supply line is provided for introducing air into the annular space between the drum and its cover. The cooling air entering, therefore, impinges radially on the drum and is distributed in the annular space between the drum and the cover. The drum is provided with a barrier labyrinth on the side remote from the shaft requiring cooling. In a known arrangement, there is a throttle labyrinth between the radial air inlet and the disc containing the cooling openings. The labyrinth reduces the pressure existing in the annular space to the value required by the consumers. This labyrinth is absolutely necessary in order to distribute the air, which is supplied at one point only, evenly over the annular space.
A disadvantage of this arrangement is that the throttle labyrinth clearance necessary is very difficult to calculate. In addition, the sealing strips making up the labyrinth are subjected to large aerodynamic loads. These conditions make it difficult to provide the correct amount of cooling air to the shaft. Finally, the flow losses occurring in the labyrinth are significant. Another unfavourable feature is that losses occur due to the braking effect of the air when it enters the rotating cooling openings. The excessively high mass flow through the barrier labyrinth is also a disadvantage. This high rate of leakage flow, which constitutes a loss, arises because the air must be introduced at a high effective cooling air pressure at the entry to the throttling labyrinth.